ES636_09 CYRUSTEK | Alldatasheet

Document overview

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Technical content

Features

  • True RMS-to-DC Conversion
  • Computes RMS of AC and DC Signals
  • Wide Response: * 1MHz Bandwidth for V RMS > 100mV
  • Auxiliary dB Output: * 50dB Range
  • Single-or Dual-Supply Operation
  • Low Cost
  • Power-Down Function
  • Low Power: 800μA typical

Description

The ES636 is a true RMS-to-DC converter. It accepts low-level input signals from 0 to 400 mV RMS complex input waveforms. It can be operated form either a single supply or dual supplies. The device draws less than 1 mA of quiescent supply current, furthermore, an enable pin is provided to turn-off the device, making it ideal for battery-powered applications. Application * Digital Multi-Meters * Battery-Powered Instruments * Panel Meter

-Vs dB BUF out BUF in COMMON Iout RL CAV ES636 N.C. N.C. N.C. SOP 14 Pin Package

Pin No Symbol Type Description

1 Vin I Measurement input

2 Enable I Chip enable, active LOW

3 -Vs P Negative supply voltage

4 Cav IO Averaging capacitor

6 BUF OUT O Buffer output

7 BUF IN I Buffer input

8 Iout O Rms output

9 R L IO RL terminal, connected to COMMON in general

10 COMMON G Analog ground

11 N.C. 12 N.C. 13 N.C 14 +Vs P Positive supply voltage Absolute Maximum Ratings Power Dissipation (Package)

(TA= +25℃, Vs = +3V , -Vs = -3V , unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS Transfer Equation VOUT = [avg.(VIN)2]1/2 Averaging Time Constant Figure 3 6 ms/μF CAV CONVERSION ACCURACY ±0.5 ±1.0 Total Error, Internal Trim (Notes 1,2) mV ±% of Reading ±0.1 ±0.01 Total Error vs. Temperature (0 ℃ to + 70 ℃) mV ±% of Reading/℃ Total Error vs. Supply ±0.1 ±0.01 mV ±% of Reading/V Total Error vs. DC Reversal VIN=+400mV DC ±2.0 ±% of Reading Total Error, External Trim (Note 1) ± 0 . 5 ± 0 . 2 mV ±% of Reading

(TA= +25℃, Vs = +3V , -Vs = -3V , unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS ERROR vs. CREST FACTOR Crest Factor 1 to 2 Specified Accuracy Crest Factor = 3 0.2 Additional Error Crest Factor = 6 0.5 ±% of Reading FREQUENCY RESPONSE (Note 2,4) VIN =35mV 75 VIN=100mV 99 Bandwidth for 1% Additional Error (0.09dB) VIN =400mV 560 kHz VIN =35mV 1.1 VIN =100mV 2.5 MHz ±3dB Bandwidth VIN =400mV 6.5 MHz INPUT CHARACTERISTICS Continuous RMS, All Supplies 0 to 400 mVRMS +3V, -5V Supplies ±2.8 ±2.5V Supplies ±2 Input Signal range Peak Transient ±5V Supplies ±5 VPK Safe Input All Supplies ±12 VPK Input Resistance 5.33 6.7 8 kΩ Input Offset Voltage ±0.5 mV OUTPUT CHARACTERISTICS (Note 1) TA=+25℃ ±0.5 mV TA =TMIN to TMAX ±10 μV/℃ Offset Voltage With Supply Voltage ±0.1 mV/V +3V, -3V Supplies 0 to 2 Output Voltage Swing ±5V to ±10V Supplies 0 to 1 1.5 V Output Resistance 8 10 12 kΩ dB OUTPUT ERROR 3mV ≦ VIN ≦ 1V ±0.3 ±0.5 dB Scale Factor -3 mV/dB %/℃ Scale Factor Tempco dB/℃ IREF 0dB=0.11V RMS 2 4 8 μA IREF Range 1 50 μA IOUT TERMINAL IOUT Scale Factor 125 μA/VRMS IOUT Scale Factor Tolerance -20 ±10 ±20 % Output Resistance 8 10 12 kΩ Voltage Compliance -Vs to (+Vs-2.0) V BUFFER AMPLIFIER Input and Output Voltage Range -Vs to (+Vs-2.0) V ±0.8 ±2 mV Input Offset Voltage Rs=10kΩ Input Current 100 300 nA Input Resistance 108 Ω Source +2 mA Output Current Sink -130 μA Short-Circuit Current 20 mA Small-Signal Bandwidth 1 MHz Slew Rate (Note 5) 3 V/μs

(TA= +25℃, Vs = +3V , -Vs = -3V , unless otherwise noted.) Power SUPPLY Rated Performance +3/-3 V Dual Supplies +2/-2.5 ±10 V Single Supply +5 +20 V Quiescent Current (Note 6) 0.8 1 mA Note 1: Accuracy is specified for 0 to 400mV, 1kHz sine-wave input. Accuracy is degraded at higher RMS signal levels. Note 2: Measured at pin 8 (IOUT), with pin 9 tied to COMMON. Note 3: Error vs. crest factor is specified as an additional error for 200mVRMS rectangular pulse input, pulse width = 200μs. Note 4: Input voltages are expressed in volts RMS. Note 5: With 10 kΩ external pull-down resistor from pin 6 (BUF OUT) to – Vs. Note 6: With BUF input tied to COMMON. Detailed Description Figure 1 shows the simplified schematic of ES636. It consists of four major subcircuits: absolute value circuit (rectifier), square/divider, current mirror and buffer amplifier. The actual computation performed by the ES636 follows the equation: VRMS = Avg. [VIN2／VRMS] The input voltage, V IN, applied to the ES636 is converted to a unipolar current I 1 (Figure 1) by the absolute-value/voltage. This current drives one input of the squarer/divider that produces a current I4 , which has the transfer function: Ι Ι= Ι The current I4 drives the internal current mirror through a low-pass filter formed by R1 and the external capacitor, CAV. As long as the time constant of this filter is greater than the longest period of the input signal, I 4 is averaged. The current mirror returns a current, I3, to the square/divider to complete the circuit. The current I4 is then a function of the average of (I12/ I4), which is equal to I1RMS. The current mirror also produces a 2 ．I4 output current, IOUT, that can be used directly or converted to a voltage using resistor R2 and the internal buffer to provide a low-impedance voltage output. The transfer function for the ES636 is: VOUT=2．R2．IRMS= VIN

output is zero when the externally set emitter current for Q5 approximates I3. Figure 1. ES636 Simplified Schematic

Figure 2. Standard connection for ES636.

z High-Accuracy Adjustments The accuracy of the ES636 can be further improved by the external trimming scheme as hown in Figure 4. The input should be grounde d and R4 adjusted to give zero output x t e r n a l G a i n a n d O f f s e t T r i m m i n g C i r c u i t . n 2). To enable the device, this pin must be s from pin 6. R1 and R2 are trimmed to give the correct value for a calibrated signal. VIN Enable CURRENT MIRROR SQUARE DIVIDER ABSOLUTE VALUE -Vs Cav + - Vout BUF 14+Vs -Vs dB COMMON BUF in BUF out RL CAV Vin +Vs +Vs Iout 500K 154 470 200 Ω Ω Ω Ω -Vs F i g u r e 3 . E Power-Down Function The ES636 provides a chip-enable pin (Pi connected to –Vs. If it is connected to V+, the device will enter power-down mode. The

current it draws at this mode is less than 1uA. average (or DC) error plus some amount of ripple. average (or DC) error plus some amount of ripple. chosen to be at least ten times the signal period. chosen to be at least ten times the signal period. Figure 4. Errors/Settling Time Graph for Standard Connection Figure 4. Errors/Settling Time Graph for Standard Connection

reduce the settling time and ripple is to use a post filter. Two suggested circuits are wn in Figure 4 and Figure 5. A post filter allows a smaller C AV. With post filter, e value of C AV should be just large enough to gi ve the maximum dc error at the west frequency of interest. And the output ripple will be removed by the post filter. level. Figure 11 present the frequency response of the converters from 35mV to 1V for ES636. , and ±3dB of reading dditional error. Caution must be used when designing RMS measuring systems so that sho th lo Figure 5(a). ES636 with a One-Pole Filter (b) with a Two-Pole Filter Decibel Output (dB) The dB output of the ES636 originates in the squarer/divider section and works well over a 50dB range. The dB output has a temperature drift of 0.03dB/℃. Frequency Response ES636 utilizes a logarithmic circuit in perf orming the RMS computation of the input signal. The bandwidth of the RMS converters is proportional to signal re The dashed lines indicate the upper frequency limits for 1%, 10% a CURRENT MIRROR SQUARE DIVIDER ABSOLUTE VALUE Cav - + -Vs +VsVin Vout BUF +Vs CURRENT MIRROR SQUARE DIVIDER ABSOLUTE VALUE Cav - + -Vs +VsVin BUF +Vs Vout C2 C3 10KΩ

overload does not occur. The input clipping level for ES636 is ±10V . A 3VRMS signal with a crest factor of 3 has a peak input of 9V . Figure 6. Frequency Response for ES636

1.14 Pin SOP Package

  1. Dimension Paramenters